In 63,752 Chinese adults, high social jetlag was more common at the week level than at the person level, and adverse associations with sleep and physical activity were driven mainly by between-person differences rather than within-person week-to-week changes.
Median sleep-corrected social jetlag (SJLsc) was 0.70 hours in this large longitudinal wearable cohort.
High social jetlag was more common at the week level than at the person level.
High social jetlag was less likely during both extended-rest and extended-work weeks compared to normal weeks.
Geographic location farther west within China was associated with later sleep timing and greater social jetlag.
Adverse associations of social jetlag with sleep and physical activity were stronger between persons than within persons.
Nocturnal heart rate variability (HRV) showed no robust association with social jetlag.
This research suggests that social jetlag—the mismatch between when people sleep on workdays versus free days—is a common but variable phenomenon in a large sample of Chinese adults. Using wearable device data from over 63,000 people across more than two million weeks, researchers found that in any given week, about 1 in 4 weeks involved significant social jetlag, even though only about 1 in 5 people had high social jetlag on average. This distinction matters because it shows that social jetlag fluctuates week to week rather than being a fixed characteristic of a person. Interestingly, during holiday weeks and weeks where weekends were converted to workdays, social jetlag actually decreased—but people in those same weeks were more likely to sleep too little, highlighting that a reduction in social jetlag does not automatically mean better sleep overall. The study also found that people living in western parts of China, where the sun rises and sets later relative to the national clock time, tended to sleep later and experience more social jetlag. This is consistent with the idea that a mismatch between the body's internal clock (anchored to sunlight) and societal schedules (anchored to standard time) contributes to circadian disruption. Regarding health outcomes, the negative effects of social jetlag on sleep quality and physical activity were mostly explained by stable differences between people rather than by changes within the same person over time. Nocturnal heart rate variability, a measure of nervous system balance, did not show a clear relationship with social jetlag. This research suggests that when evaluating social jetlag in health contexts, it is important to consider both a person's typical pattern and the specific schedule context of any given week, since the same level of social jetlag can mean very different things depending on whether it coincides with short sleep or unusual work schedules. The large-scale wearable data approach provides a more nuanced picture than traditional survey-based studies, pointing to the value of separating stable individual traits from week-to-week fluctuations when studying sleep and circadian health.
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Upload Your LabsFu X, Ma K, Yu M, Xu Y, Chen Y, Huang Z, et al.. (2026). Social jetlag in a longitudinal Chinese wearable cohort: weekly variation, solar-time mismatch, and sleep-activity associations.. Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine. https://doi.org/10.1007/s44470-026-00209-1